Customer acquisition cost cuts will significantly lower the price of solar, according to Litvak. "Residential solar customer acquisition currently costs installers $0.49 per watt,” her study found. “Over the next four years, this cost will fall to $0.35 per watt, saving the industry a total of $619 million between 2014 and 2017.”

Picking the right emerging solar markets is another lynchpin of the REC Solar growth strategy, Miller said. “We don’t want [to bother with] flash-in-the-pan markets, so we’re not always the first into a market. When we go in, we are there for the long run.” In 2013, REC Solar focused on the quadrupling California Inland Empire market, as well as New York and Hawaii.

While 40 percent of solar install orders are canceled industry-wide, only 5 percent of REC Solar’s customers cancel. “When we qualify customers, we are honest and educate them about solar,” Miller explained. “That way, we are more likely to meet their expectations.”

Marketing companies from outside of residential solar are coming, Clean Power Finance CEO Nat Kreamer recently observed, and that will drive growth up and customer acquisition costs down.

An example would be Vivint Solar, which has installed home security systems nationally for twenty years, has big media ties, and has become the second-largest national installer over the last eighteen months. “We acquire customers. That’s what we do," Vivint VP Thomas Plagemann recently said. "We took that customer acquisition engine and applied it to solar.”

The biggest and most cost-effective part of REC Solar’s growth may have come from its strong retail partners program.

“Retail partnerships are one of the most important emerging trends in the residential solar market,” wrote Litvak in her report on customer acquisition. The biggest successes come from placing sales representatives in home improvement stores. SolarCity and Roof Diagnostics are at Home Depot, and Sungevity is at Lowe’s.

The cost per lead is higher than it is for referrals, but such partnerships generate more leads and a higher conversion rate, Litvak wrote. Retail partnerships are, however, “much more difficult to establish, as they generally involve larger corporations and therefore a more complicated negotiation process," she explained.

“We look for companies that have similar values,” Miller said of his company’s successful retail partnerships. REC Solar has one “major national big-box retail partner,” he said, which, because of “brand sensitivity,” he declined to name.

Another partnership strategy is with local merchants, Miller said. “If a community has a bath and kitchen retailer with six outlets, we can set up kiosks in their store or parking lot. The sales consultants manning the kiosks can be more effective because they are local. They know the community. They may be members of the Chamber of Commerce, or a customer may trust them because they met at a PTA meeting.”

REC Solar has twenty locations across the country and a sales and field marketing team of several hundred people. Its cost of customer acquisition is very close to the published national average of $0.49 per watt, according to Miller.

“Investing in new tools, in new methods of lead generation like canvassing, and in phone and online marketing can drive growth, but that comes with other sacrifices," he explained. "We want to have the lowest cost, but we want to balance that with our values.”

Finally, some of REC Solar's growth came from providing third-party ownership opportunities for low- and no-down-payment financing, Miller said. That will continue to be where the bulk of the installs are going forward, he added, and REC Solar will get them through its partnerships with Sunrun and Clean Power Finance.